Image output devices that create dots on various output media, such as printing media and liquid crystal screens, to output images have been used widely as output devices of diverse imaging devices. The image output device processes each image as a collection of very small areas called pixels and creates dots in these pixels. Each pixel individually takes only one of two dot states, that is, dot-on state and dot-off state. The density of dot creation may be varied in a relatively wide image area. The varying dot creation density enables output of a multi-tone image. For example, in the case of creation of black ink dots on printing paper, areas of dense dot creation are darker and areas of sparse dot creation are brighter. In the case of creation of dots as bright points on a liquid crystal screen, areas of dense dot creation are brighter and areas of sparse dot creation are darker. The adequate regulation of the dot creation density enables output of a multi-tone image. An object image to be output goes through a preset series of image processing to give control data for creation of dots at adequate densities.
The latest requirements for these image output devices are size enlargement and enhanced picture quality of output images. Division of an image into smaller pixels is an effective measure for the enhanced picture quality requirement. The smaller pixels make the respective dots created in the pixels inconspicuous and thereby improve the picture quality. Increasing the number of pixels is an effective measure for the size enlargement requirement. The increased dimensions of the respective pixels naturally enlarge an output image but undesirably lower the picture quality of the output image. The increased number of pixels is thus effective for the size enlargement of the output image.
The increased number of pixels constituting an image, however, undesirably extends the time of image processing and interferes with high-speed image output. Various techniques have accordingly been proposed to attain high-speed image processing (for example, Japanese Patent Laid-Open Gazette No. 2002-185789).
The high-speed image processing alone is, however, not sufficient to attain the high-speed image output. Another requirement is thus high-speed transfer of original image data and processed image data.
With the wide spread of digital cameras, there is a requirement of direct supply of image data taken with a digital camera to a printing device or another image output device for immediate image output. In such cases, a personal computer or another image processing device of high throughput is not usable for the required image processing. The image processing should thus be simplified to be executable by one or both of an imaging device, such as a digital camera, and an image output device, which are generally of relatively low throughput.